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In this paper, we report Soret coefficients obtained by two independent methods and for two different systems-(water-ethanol containing respectively 60.88 and 50 wt % of water). The Soret coefficient is defined by S T ) D T /D where D T is the thermal diffusion coefficient, and D is the isothermal diffusion coefficient. In the first method, D T is determined by a 5-point sampling process in a thermogravitational column and D by the well-known OEC technique (open-ended capillary). The ratio of the experimental values of D T and D gives the expected value of S T . A totally new method consists of velocity measurements of a transient natural convective state: indeed, the Soret effect induces modifications of density gradients and therefore of the buoyancy responsible for free or natural convection. The modifications of the convective amplitudes are thus an indirect way to have access to the Soret coefficient. The velocity measurements were obtained by LDV. The comparison between the two techniques shows a deviation of the order of 4%, which is quite satisfactory. The agreement with the literature is also excellent.

Thermal diffusion coefficients in three ternary mixtures are measured in a thermogravitational column. One of the mixtures consists of one normal alkane and two aromatics (dodecane-isobutylbenzene-tetrahydronaphthalene), and the other two consist of two normal alkanes and one aromatic (octane-decane-1-methylnaphthalene). This is the first report of measured thermal diffusion coefficients (for all species) of a ternary nonelectrolyte mixture in literature. The results in ternary mixtures of octane-decane-1-methylnaphthalene show a sign change of the thermal diffusion coefficient for decane as the composition changes, despite the fact that the two normal alkanes are similar. In addition to thermal diffusion coefficients, molecular diffusion coefficients are also measured for three binaries and one of the ternary mixtures. The open-end capillary-tube method was used in the measurement of molecular diffusion coefficients. The molecular and thermal diffusion coefficients allow the estimation of thermal diffusion factors in binary and ternary mixtures. However, in the ternaries one also has to calculate phenomenological coefficients from the molecular diffusion coefficients. A comparison of the binary and ternary thermal diffusion factors for the mixtures comprised of octane-decane-1-methylnaphthalene reveals a remarkable difference in the thermal diffusion behavior in binary and ternary mixtures.

We report on the measurement of diffusion (D), thermodiffusion (D(T)), and Soret (S(T)) coefficients in water-isopropanol mixtures by three different instrumental techniques: thermogravitational column in combination with sliding symmetric tubes, optical beam deflection, and optical digital interferometry. All the coefficients have been measured over the full concentration range. Results from different instruments are in excellent agreement over a broad overlapping composition (water mass fraction) range 0.2 < c < 0.7, providing new reliable benchmark data. Comparison with microgravity measurements (SODI/IVIDIL (Selected Optical Diagnostic Instrument/Influence of VIbration on DIffusion in Liquids)) onboard the International Space Station and with literature data (where available) generally gives a good agreement. Contrary to theoretical predictions and previous experimental expectations we have not observed a second sign change of S(T) at low water concentrations.